Which key point is most difficult to control in the tempering curve of H13 material?

The temperature homogeneity inside the furnace is the most challenging essential point to control in the tempering curve of H13 material. The hardness difference of workpieces in the same batch will exceed the standard (>2 HRC) even with exact temperature settings if there are temperature variations within the furnace (e.g., hotter at the top and colder at the bottom, or uneven temperature at the corners), which will significantly affect performance consistency.

 

1. What makes controlling temperature consistency the most challenging? Factors & Reasons:

Equipment Aging Has a Big Impact: In older furnaces, thermocouple drift and damaged insulation layers can result in localized temperature variations that are hard to identify in real time.

Workpiece stacking or spacing of less than 5 cm might impede heat circulation, resulting in "cold zones" and "hot zones." This makes the factory loading method sensitive.

Inadequate Temperature Measurement Coverage: Just keeping an eye on the furnace chamber's center temperature does not accurately represent the temperature in the corners or at the bottom.

Uneven Heating and Cooling Rates: When heating quickly, the core takes longer to attain temperature than the surface, which results in temporary unevenness.

Real-world Example: An ancient box furnace was used in a factory. The bottom workpieces only measured at 568°C, which caused the hardness to decline from 50.2 HRC to 47.8 HRC despite being set to 580°C. As a result, the entire batch was destroyed.

 

2. Comparing the Difficulties of Controlling Temperature Uniformity

Important Points

Causes

Uniformity of Furnace Temperature

largely hidden and influenced by a number of variables, such as furnace loads, equipment, and temperature measurement configuration

Adjusting the Temperature

PID systems can be set precisely, but they need to be calibrated on a regular basis.

The quantity of temperings

Simple to carry out; single action; no chance of ongoing volatility

Keeping Time

Clear formula for increasing the holding time for thick parts and programmable control

Core Challenge: The systemic issue of temperature uniformity necessitates coordinated equipment, process, and operation improvement.

 

3. Doable Steps to Boost Uniformity

Multi-point temperature measurement verification: To guaranty a temperature difference of ≤ ±5°C, place ≥6 temperature measurement points in the furnace's upper, middle, lower, front, back, and corners;

Standardized furnace loading: minimize direct stacking, utilize tooling racks robust to high temperatures, and space workpieces at least 5 cm apart;

Furnace temperature uniformity testing (TUS): Conducted on a quarterly basis and assessed in accordance with the AMS 2750 standard;

Segmented heating control: To lessen thermal stress and temperature differential, gradually raise the temperature (≤150°C/h) while it is below 400°C.